Which of the following is the investigation of choice for Reversible Myocardial Ischemia?

Thallium 201 is a photon-emitting substance with biologic propeies similar to potassium. It can concentrate inside cells that function normally. Regions that are ischaemic or dead do not concentrate thallium and appear as defects on the scan. Reversible ischemia, such as that induced by exercise, is marked by defects seen at peak exercise that later fill on the delayed scans (reversible defects). In contrast, dead or infarcted regions appear as defects in both exercise and delayed scans (fixed defects). Ref: Medicine By Mark C Fishman, 5th Edition, Page 12; Harrison's Principles of Internal Medicine, 16th Edition, Pages 1324-26